This invention relates to an automatic gain control circuit for use in those receivers which effect an intermittent reception operation, such as a pager.
To eliminate intermodulation distortion and disturbance at the time of reception of a large input signal, a one-stage automatic gain control system has been employed in the past in FSK signal intermittent receivers such as a pager, as described in JP-A-2-308606.
The prior art system described above is mainly directed to improve intermodulation distortion characteristics at the time of a large input signal.
However, this automatic gain control system switches a gain in only one stage and holds a received signal. Therefore, this system involves the problem that gain control cannot be made in accordance with input levels over a broad range from a small input signal to a large input signal, and intermodulation distortion and disturbance, which become a practical problem, cannot be improved sufficiently. Further, this system can set only one detection point of a reception field level for gain control. Accordingly, since a reception sensitivity point after the gain control must be set to a field level lower than the field level at the detection point, the upper limit of the gain control quantity is unavoidably limited. In consequence, the gain control cannot be made sufficiently at the time of an excessive input level and intermodulation distortion characteristics become inferior.